Too much boost which will cause melt down in #6 and #4 to follow. Will happen everytime..

I understand, but I am at 6psi and I have changed nothing. This was a 30 sec full throttle run and the temp was at 130 degrees. I have had this same setup for 7 years now and all of the problems I have had were due to the stock cast heads. Why all of a sudden is this a problem, that is the $10,000 question. I have ran full throttle at LOTO racing for miles on end without any problem.

yes, the KB are blower pistons about 8-1 but the tops are thicker to stand up under boost and the rings are moved down in most cases, you will need to balance the engine at this point don't skimp there or bad thing may just happen again...

Nothing lasts forever.......maybe it was time.

after that much time on the engine the ring seal may have went away letting oil into the cumbustion chamber which could cause preignition/detonation. that being said it would up the octane requirement. safe bet would to be upgrade the fuel system also a drop in compression and total timing would give a little edge for the variation of fuel quality available. definately go forged as supercharged engines are always on the edge of detonation/preignition at higher rpm

I have a nice set of gently used 509 pistons JE

Back about 4 or 5 years ago I blew a hole in a piston. I was using a flat tappet cam and a few of the lobes went down. That caused a piston to go lean and boom!! The root cause of the problem was the oiling system. I had upgraded to about 450HP and I had the stock 330 cooler and lines.

I know, there are many possible reasons. So I plan on upgrading the fuel system.
JCPERF, what is the pn: of those pistons, and what exactly does (gently used) mean? How many hours are on them. My instinct is to start with new though.